Can anyone explain Weekender fares?

[childss]

I was delighted to discover recently that the Weekender tickets offered great discounts on the train to Galway -- the ticket costs 29 compared with 44 normally -- a saving of 35%. However on the Limerick route which I get more often, the Weekender is 44 and the full price is 50 -- a saving of only 12%. Why is there such a difference? (I won't ask why the Limerick route costs more in the first place than Galway and Sligo which are further away.)

Also, why is the Weekender ticket not promoted in any way? I've told loads of people about it and no-one has ever heard of it. Even on the under-discounted Limerick route it almost pays for itself first time out.